The use of light probes at discrete locations in a scene is a common and efficient way to estimate the diffuse global illumination at other points in the scene. Specifically, irradiance is sampled at each probe and encoded for each of a plurality of directions, and this pre-computed information is retrieved at run-time rather than being computed on the fly. If the point at which the diffuse global illumination is to be determined is located between multiple probes, the technical problem becomes one of selecting which probes are to be considered most influential to the computation of the diffuse global illumination. In this regard, known methods interpolate probes based on their proximity to the point of interest. However, this fails to take into consideration the effect of occlusion that certain elements in the scene may have, which results in certain nearby probes being unduly influential in their contribution to diffuse global illumination at certain points in the scene. As a result, the viewer may perceive unpleasant artifacts such as “popping”.